Sex roles, parental experience and reproductive success of eastern kingbirds, Tyrannus tyrannus

We quantified parental behaviour of eastern kingbirds during the incubation and nestling periods to determine parental roles, and to examine the impac t of previous breeding experience (defined as having bred on the territory in the past) on behaviour and reproductive success. Females performed all i ncubation, while males spent more than 60% of their time in vigilant or nes t guarding behaviour during incubation. Parental roles were not defined as sharply during the nestling period. Females spent more time vigilant, but m ales provisioned young at only 54% of the rate of females. Vigilance and ne st watching were still primarily male duties. Male and female behaviour did not vary with the pair's combination of experience (e.g. experienced-exper ienced versus inexperienced-inexperienced in previous-current breeding seas on, respectively) during either phase of reproduction, but experienced male s were more vigilant during incubation and fed young relatively more than i nexperienced males. Experienced females were also more efficient foragers. Although behaviour did not differ among the four combinations of pair exper ience, inexperienced pairs none the less lost the most young to starvation and predation. Consequently, inexperienced pairs fledged one less nestling per nesting attempt than did pairs with at least one experienced breeder. O ur results suggest that having at least one experienced breeder substantial ly improved a pair's reproductive success. We propose that female site fide lity is a safeguard to avoid the lower breeding success a female would incu r if she were to move to a new territory and breed with an inexperienced ma le. (C) 1999 The Association for the Study of Animal Behaviour.